1. Field of the Invention
The present invention relates to a controller for avoiding interference between a mold or ejector and a product removing unit in an injection molding machine.
2. Description of the Prior Art
Some injection molding machines have a product removing unit for removing a product molded by using a mold. This product removing unit, which removes a molded product automatically, is configured by a robot or a special-purpose product removing unit. The product removing unit must be operated in association with the injection molding machine, so that the operation timing of the product removing unit is set so as to match the operation timing of the injection molding machine.
Generally, when the product removing unit begins its operation upon receipt of a mold opening finish signal after a mold has been opened and finishes removing a molded product, a product removal finish signal is sent to an injection molding machine. Upon receipt of this product removal finish signal, the injection molding machine starts the next molding operation, that is, a mold closing or mold clamping operation.
In the above-described general method for removing a molded product, the product removing unit starts its operation after waiting until the mold has opened completely, and the injection molding machine starts the mold closing operation for the next molding cycle after waiting until the product removing unit has removed the molded product completely. Therefore, the waiting time consumes time wastefully, and the cycling time for molding is prolonged.
To reduce this waiting time, there is used a method for controlling the operation of the product removing unit in synchronization with the mold opening/closing operation, in which a signal is generated before the opening of mold is finished, the operation of the product removing unit is started by this signal, and a signal is sent to the injection molding machine before the removal of molded product is finished by the product removing unit, by which the mold closing operation is started. For example, Japanese Patent Application Laid-Open No. 62-273816 describes an invention in which the operation of the product removing unit is controlled according to the mold travel amount in mold opening operation so that when the mold opening is finished, a holding portion of the product removing unit is moved so as to reach a position where a molded product can be removed, and when the movable mold moves in the mold clamping direction, the product removing unit is controlled according to the travel amount of movable mold to retreat the holding portion from the position where the molded product is removed.
With the above-described method in which the operation of the product removing unit is controlled in synchronization with the mold opening/closing operation of the injection molding machine, it is very difficult to adjust the operation timing of the product removing unit. The operation start timing changes each time the opening/closing speed of mold or the operation speed of the product removing unit changes, so that readjustment is needed. Also, if a bit unnatural operation is effected, a hand etc. of the product removing unit gets caught in the mold, whereby the expensive mold or hand is damaged. Therefore, in order to adjust the timing of operation start etc., a test must be conducted repeatedly. That is, the operation start timing of the product removing unit at the time of mold opening and the mold closing operation timing must be determined by transmitting signals between the injection molding machine and the product removing unit. If this work is incorrect, there is a fear of damaging the mold, hand, etc., so that this work must be done carefully, which requires much time and long-term experience.